Historically, enclosures for electrical equipment, such as circuit breaker panel boards or load centers, have invariably been formed from metal. These metallic enclosures are usually manufactured in mass-production from metal sheets in a succession of operations, including cutting, blanking, forming and welding, to create a box-like housing, which usually is then painted. The enclosure covers are produced in a similar fashion in a succession of operations, and a number of components, including component-mounting and supporting elements, must then be assembled into the box-like housing. Since the metallic enclosure is electrically conductive, insulators must be used for mounting the various bus bars within the enclosure.
In recent years, there has been significant activity in the direction away from the utilization of such metal enclosures for distribution load centers. For example, U.S. Pat. No. 3,801,875 discloses a non-metallic load center molded plastic enclosure consisting of a housing that has integrally-formed back and side walls and a separate cover. The construction of the load center disclosed therein is such that the bus bars are mounted on molded posts that are formed integrally with the back wall of the housing. However, such an arrangement still requires a number of assembly steps and also requires a very specific construction for the bus bars to provide the necessary contact.
More recently, U.S. Pat. No. 4,698,727 proposes a compact, non-metallic load center enclosure or molded plastic load center that includes a plastic casing that has a plastic cover attached thereto to which a plastic door is mounted through a hinge assembly. The case receives a circuit breaker support assembly that consists of a non-metallic support member and specially-configured bus bars that must be manufactured from a number of pieces and require a number of welding steps.
Other examples of extruded plastic components for load centers are shown in U.S. Pat. Nos. 4,536,823 and 4,118,754.